U.S. Pat. No. 4,496,395, entitled "High Coercivity Rare Earth-Iron Magnets", assigned to the assignee hereof, discloses novel magnetically hard compositions and the method of making them. More specifically, it relates to alloying mixtures of one or more transition metals and one or more rare earth elements. The alloys are quenched from a molten state at a carefully controlled rate such that they solidify with extremely fine grained crystalline microstructures as determinable by X-ray diffraction of powdered samples. The alloys have room temperature intrinsic magnetic coercivities after saturation magnetization of at least about 1,000 Oersteds. The preferred transition metal for the magnet alloys is iron, and the preferred rare earth elements are praseodymium and neodymium. Among the reasons why these constituents are preferred are their relative abundance in nature, low cost and inherently higher magnetic moments.
I have now discovered a new family of magnets that have markedly improved properties compared with my earlier discovery. It is an object of the subject invention to provide novel magnetically hard compositions based on rare earth elements and iron with extremely fine grained crystal structures having very high magnetic remanence and energy products and Curie temperatures well above room temperature. Another object is to create a stable, finely crystalline, magnetically hard, rare earth element and iron containing phase in melted and rapidly quenched alloys so that strong permanent magnets can be reliably and economically produced.
A more specific object is to make magnetically hard alloys by melting and rapidly quenching mixtures of one or more rare earth elements, one or more transition metal elements and the element boron. Such alloys exhibit higher intrinsic coercivities and energy products than boron-free alloys. A more specific object is to make such high strength magnet alloys from iron, boron and lower atomic weight rare earth elements, particularly neodymium and praseodymium. Another object is to make these magnetically hard alloys by melt spinning or a comparable rapid solidification process.
Yet another object of the invention is to provide a novel, stable, rare earth-iron-boron, intermetallic, very finely crystalline, magnetic phase. A more particular object is to control the formation of such phase so that the crystallite size appears to be commensurate with optimum single magnetic domain size either by a direct quench or overquench and subsequent heat treatment. Another particular object is to either directly or indirectly create such optimum domain size crystallites in a melt spun or otherwise rapidly quenched RE-Fe-B alloy, particularly a neodymium or praseodymium-ironboron alloy.
It is a further object to provide a suitable amount of boron in a mixture of low atomic weight rare earth elements and iron to promote the formation of a stable, very finely crystalline, intermetallic phase having high magnetic remanence and energy product. Another particular object is to provide the constituent metallic elements in suitable proportions to form these new intermetallic phases and then process the alloys to optimize the resultant hard magnetic properties.